1. Field of the Invention
The invention relates generally to a digital chromakey apparatus. More particularly, although not exclusively, this invention relates to a digital chromakey apparatus in which a key signal can be adjusted to compensate boundary between foreground scene and background scene to be inserted.
2. Description of the Prior Art
A known digital video signal processing apparatus such as a digital chromakey apparatus and a digital montage apparatus has to form a key signal corresponding to a part of areas in one picture. The reason for this is as follows. The known chromakey apparatus is of a construction as shown in FIG. 1. In the figure, references 1 and 2 denote color television cameras, each of which is used to take pictures of foreground and background. References 3 and 4 denote gate circuits to which foreground and background color video signals are respectively supplied. Reference 5 denotes a key signal generator to generate and supply the key signal to the gate circuits 3 and 4. Reference 6 denotes a mixer to mix the outputs of the gate circuits 3 and 4 produce the mixed output at an output terminal 7.
By way of example, as shown in FIG. 2A, a foreground 10 in which an object 9 (for example, human figure) is positioned in front of a back screen 8 painted with a back color of, for example, blue is photographed or picked up by the color television camera 1 and then, the key signal generator 5 calculates three primary color components R, G and B in the above foreground color video signal so as to convert the color phase difference to the amplitude difference thus forming the key signal. In other words, as shown in FIG. 2C, the key signal which makes the gate ON only in the part of the object 9 is formed and supplied to the gate circuit 3, while as shown in FIG. 2D, the key signal which makes the gate ON only in the part other than the object 9 is formed and then supplied to the gate circuit 4. Therefore, the background picture 11 photographed by the television camera 2 as shown in FIG. 2B, is cored by the part corresponding to the object 9 in the gate circuit 4 and the picture signal shown in FIG. 2E is mixed with the picture signal, indicating the object 9.
Thus at the output terminal 7 there is generated a picture signal in which the object 9 is inserted into the background 11 as shown in FIG. 2F.
But, in such prior art chromakey apparatus, the edge portions of the key signal thus produced do not always correspond to the boundary or border between the back screen 8 and the object 9. To cope with the above aspect, the timings of the edge portions of the key signal have to be adjusted.